1. Field
Embodiments of the disclosure relate generally to the field of mating systems for structural access doors and more particularly to a system for alignment and providing mistake resistance for fuel tank access doors with features for pressure distribution to avoid tank seal breech.
2. Background
Structural access doors in large commercial aircraft are required to provide ingress and egress from various compartments such as wing fuel tanks for maintenance and inspection requirements. The doors are typically designed with fastener systems (with self-retained nuts) and have minimal surface protrusion on the outer surface to provide aerodynamic smoothness for the door surface. In large aircraft a significant number of wing access doors are present, many with similar or identical size and planform. These wing access doors are designed to differing strengths depending on where on the wing the door is placed. For instance doors near the landing gear tires must withstand large pieces of rubber and debris that can collide with the door after tire failure. Doors that are further way from the tires do not need to be as strong and so a lighter and, consequently, weaker door is made. To assure that certain doors are not installed at incorrect locations, some type of physical mistake resistance is required. This insures that the medium or light doors are not used in areas where heavier doors are required. In certain prior art systems radial blade and slot engagement of mistake resistance features has been employed.
Additionally, aircraft are susceptible to electrical discharges due to static or other natural phenomena, particularly with respect to wing fuel tank access doors, control or diversion of the energy from electrical discharges is required. In prior art aircraft having metallic structure, conductive paths provided by the structure itself typically rendered sufficient protection. However, with greater reliance on composite structural materials which are generally less conductive than metals typically used in commercial aerospace, alternative design methods are required. One embodiment of a prior art door design for use in carbon fiber reinforced plastic (CFRP) structures employed a conductive clamp ring mounted against a conductive door surface to allow currents to flow across the door and wing surface. In advanced aircraft designs, use of CFRP for greater portions of the structural content of the aircraft is desired for further weight reduction. A change from metal to CFRP as the primary access door material and removing the clamp ring from the design is there for desirable. Not having a continuous conductive path between a door retention fastener to the door surface to the wing skin may lead to an electrical discharge. This may result in expanding gas in the volume between the inner/outer doors and the access hole wing skin cutout (“racetrack”).
It is therefore desirable to provide access door interface designs for (CFRP) structures which provide the desired mistake resistance and avoid impeding any expanding gas in the racetrack thereby preventing redirection of the gas with possible seal breech into the fuel tank.